Power converter circuits may be used to convey power from a source, such as a battery, electrical power grid, etc. to a load, such as any device, apparatus, or component that runs on electricity, preferably with as little loss as possible. Generally, a power converter circuit provides an output voltage that has a different level than the input voltage. One type of power converter circuit is known as a switching or switched mode power supply. A switched mode power supply controls the flow of power from a power source to a load by controlling the “on” and “off” duty cycle of one or more transistor switches in order to regulate the DC output voltage across the output terminals of the power supply. The “on” and “off” duty cycle of the one or more transistor switches may be controlled in response to a pulse-width-modulated (PWM) gate drive signal provided by a switching regulator circuit, such that the “on” and “off” duty cycle of the one or more transistor switches is determined by relative pulse-widths of the PWM signal.
Some switched mode power supplies may use a transformer or an inductor as an energy transfer element. A power transistor may be coupled to one side of the primary winding of a transformer, and may be turned on and off in response to the gate drive signal provided by the switching regulator circuit to alternately store energy in the magnetic field of the transformer and transfer the stored energy to the secondary winding. The secondary winding of the transformer may develop a rectified output voltage across a shunt capacitor coupled across the secondary winding as a function of the energy transfer. The voltage across the capacitor may provide the DC output voltage of the switching power supply. The DC output voltage, or a representation thereof, may be fed back to the switching regulator circuit to allow the switched mode power supply to compensate for load variation. As the load increases, the DC output voltage decreases, which may cause the switching regulator to alter the gate drive signal to leave the power transistor “on” for a longer average period of time in order to store more energy in the magnetic field. The additional energy may be transferred to the secondary winding during the “off” time of the power transistor to supply the increased load and re-establish the DC output voltage. As the load decreases, the DC output voltage increases, which may cause the switching regulator to alter the gate drive signal to leave the power transistor “on” for a shorter average period of time to store less energy in the magnetic field. The reduced energy transfer to the secondary winding during the “off” time of the power transistor may cause the power supply to adjust to the decreased load and may reduce the DC output voltage back to its steady-state value.
Switched mode power supplies have been implemented as an efficient mechanism for providing a regulated output, and are generally more power efficient than linear voltage regulators, which dissipate unwanted power as heat. However, many switched mode power supplies may not be able to detect overload or fault conditions. Examples of possible faults may include a short-circuit or open-circuit at the output of the power supply, broken or unpopulated magnetic components, and/or loss of power to be converted at the input of the power supply.